This invention relates to wayside protection switching for a SONET/SDH radio communication network comprising a plurality of radio communication terminals and a plurality of repeaters intermediate the communication terminals.
SONET and SDH are standards for a multiplexing format for a Synchronous Optical Network. SDH is a Synchronous Digital Hierarchy.
In a SONET/SDH radio system, besides the main traffic, additional traffic can also be transmitted and carried in the main traffic overhead bytes, such as wayside (DS-1 capacity), Service channel (DS-0 capacity) etc. See ITU-RF 751-1, section 4.1.2., 1992-94. In the present invention, protection switching of wayside traffic is used as described hereinafter.
The additional traffic could consist of more than one tributary depending on the main traffic overhead capacity. To simplify the description, protection switching of two wayside tributaries is discussed and illustrated herein as examples.
The main traffic's protection switching mode is 1:n, where n is an integer greater than 1, e.g. 1 for 11. The wayside protection switching mode of this invention is 1+1.
In the present invention, when a wayside signal enters an ADD site, it is bridged to two radio channels, resulting in two adjacent channels carrying the same wayside data. This redundant configuration makes protection switching possible by selecting the better of the two radio channels when dropping the wayside traffic to a customer. The wayside radio path is protected by using unused bandwidth from an adjacent radio channel to transport a copy of the wayside data. This constitutes a redundant radio path for the wayside data. The SOA (Service Overhead Access) circuit pack is protected by having a redundant SOA circuit pack from which the wayside can be selected at a site where the wayside is dropped.
A radio communication network is subject to radio channel impairment from a variety of causes such as electrical interference, faulty equipment or radio fading. In such cases, it is necessary to have affected communication channels switched to a radio protection channel. In the case of a pair of main radio traffic terminals, switching to the protection channel (1 for n channels) is performed by a radio signal processor at the receive terminal site if a threshold value is exceeded for either line FEC (Forward Error Correction) or line PEC (Parity Error Count). FEC is a count of the number of corrected errors. The line FEC and line PEC are calculated based on the entire traffic, namely payload and overhead, and are an accumulation of section FEC and PEC from the start terminal to the end terminal.